Studies evaluating the relationship of serum digoxin concentrations (SDCs) with pharmacodynamic effects in atrial fibrillation have important limitations. In general, a poor correlation is found between SDC and ventricular rate, but this is understandable, considering the many other factors that affect conduction through the atrioventricular node.
The ventricular rate, although a clinically important and easily monitored parameter, may not always be a good measure of digoxin effect. In certain patients, signs and symptoms of toxicity may develop before the desired decrease in heart rate. The SDC may provide, in many cases, information that cannot be obtained solely from the clinical response, but is of great relevance to therapeutic decision making.
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